PEGMATITES IN SOUTHEASTERN BRAZIL

ESSAÏD BILAL, JOSÉ MARQUES CORREIA NEVES, KAZUO FUZIKAWA, ADOLF HEINRICH HORN, VITÓRIA RÉGIA PERES DA ROCHA OLIVEIROS MARCIANO, MARIA LOURDES SOUZA FERNANDES, JAQUES MOUTTE, FERNANDO MACHADO DE MELLO, MOHAMED NASRAQUI

Resumo


Two pegmatite groups are represented in southeastern Brazil. The first group, resulting from fractional crystallization, is linked to syn-tectonic granites (580 Ma – deformation event D1) and the second one is associated with another partial melting event of the crust which simultaneously produced porphyritic leucogranites [(520-500 Ma)- later deformation event D2 ] and pegmatites themselves. The Fe/Mn ratios of tourmalines, micas and columbite-tantalites decrease continuously from simple pegmatites to gem quality elbaite-rich ones. The Fe/Mn ratio has been used as a qualitative fractionation index which seems to reflect the regional zoning of the first pegmatites group around a hidden granite body. The Fe/Mn ratio values correlate negatively with Na and Li contents in tourmalines and mica. The REE, Nb, Co and Zn contents in tourmalines, micas, and columbite-tantalites are controlled by their mineral assemblages.

Palavras-chave


Schorl;Elbaites; Gems; Columbite-tantalite; Li-pegmatites; Minas Gerais-Brazil.

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